fruitful discussions, Guanghan Cao and Zhicheng Wang for assisting with 3 He-SQUID measurements, and Xiaoyan Xiao for assistance with single crystal x-ray diffraction.

Each discovery of a new high temperature superconductor drives the expectation that advanced engineering of materials defect structures will enable effective vortex pinning and high values of the electrical current density. Here, we demonstrate that single crystals of the iron-based superconductor Ba0.6K0.4Fe2As2 with Tc = 37.5 K can accommodate an unprecedented large concentration of strong-pinning defects in the form of discontinuous nm-sized nanorods with no degradation of the superconducting transition temperature. At a temperature of 5 K, we find a critical current density of 5 MA/cm2 that is magnetic field independent in fields up to 7 T.

Mixed pinning landscapes in superconductors are emerging as an effective strategy to achieve high critical currents in high, applied magnetic fields. Here, we use heavy-ion and proton irradiation to create correlated and point defects to explore the vortex pinning behavior of each and combined constituent defects in the iron-based superconductor Ba0.6K0.4Fe2As2 and find that the pinning mechanisms are non-additive. The major effect of p-irradiation in mixed pinning landscapes is the generation of field-independent critical currents in very high fields. At 7 T ‖ c and 5 K, the critical current density exceeds 5 MA/cm2.

We report the discovery of a new noncentrosymmetric superconductor CaPtAs. It crystallizes in a tetragonal structure (space group I41md, No. 109), featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis (a = b = 4.18Å, and c = 43.70Å). The superconductivity of CaPtAs with Tc = 1.47 K was characterized by means of electrical resistivity, specific heat, and ac magnetic susceptibility. The electronic specific heat Ce(T )/T shows evidence for a deviation from the behavior of a conventional BCS superconductor, and can be reasonably fitted by a p-wave model. The upper critical field µ0Hc2 of CaPtAs exhibits a relatively large anisotropy, with an in-plane value of around 204 mT and an out-of-plane value of 148 mT. Density functional theory calculations indicate that the Pt-5d and As-4p orbitals mainly contribute to the density of states near the Fermi level, showing that the Pt-As honeycomb networks may significantly influence the superconducting properties. PACS number(s):